Electric stimulation and low-power laser devices principally dominate the field of evoked response stimulation. However, several other devices may be utilized as stimulation sources such as devices using magnetic and electromagnetic fields, non-coherent light, acoustic energy sources, and electrical or mechanical impulses.
A rather limited range of modulation schemes have been used to control the above mentioned devices. Pertinent references include the following: U.S. Pat. No. 3,085,566 to Tolles which describes a measuring device wherein a pair of sinusoidal electrical wave forms may be applied either singly or summed together as phasors such that the patient receives the vector sum of both waveforms. U.S. Pat. No. 3,900,020 to Lock describes an electric acupuncture device which employs two oscillators and is arranged so that each oscillator can be applied to separate needles or probes such that no common ground exists between the outputs of the oscillators. This design permits no interaction between the oscillators. U.S. Pat. No. 4,052,978 to Eugenio describes an electrotherapy apparatus which employs a single low frequency oscillator and detection means to locate and treat diseased organs by the application of electrical currents. U.S. Pat. No. 4,112,923 to Tomocek describes an antonomic transcutaneous affect device which employs a single oscillator and controls for timing, intensity, frequency, and waveform polarity. In addition, a circuit is provided to locate desired acupuncture points. U.S. Pat. No. 4,589,417 to Eseifan describes an apparatus for selective measuring and treating disordered tissues which employs a single oscillator in conjunction with a sensing device to establish and treat specific acupuncture points.
In addition the European market has a device which employs a chain of monostable oscillators to allow independent adjustment of pulse repetition rate, pulse train on time, pulse train off-time, and insertion of intermediate pulses between pulse trains. This device employs a pulse repetition rate modulator control unit which is separate from the CW laser unit and which was originally designed to be used for direct electrical stimulation with the laser interaction as an after thought. The pulse width of this modulator is fixed in the design and not under operator control. Laser output amplitude is, however, manually adjustable.
At the present time, this area of the art includes biostimulation lasers which can be divided into: Continuous Wave (CW) lasers (employing tubes or solid state CW diodes), Pulse Lasers (employing Q switching or solid state pulse diodes). In addition, each of the above two categories can be divided into species by modulation to include: binary scaled pulse repetition rate dividers, analog (music, noise, or tone), and variable on/off modulation.
In general, CW lasers are available with either no modulation or with variable frequency (e.g., on/off) modulation. Pulse diode lasers are virtually all of the binary scaled divider type (usually employing 7 or 8 fixed divide-by-2 scaling options), However, there is no clear-cut line. And, units are available with some of these simple modulation options and with independent CW and Pulse laser sources controlled from a single enclosure.
The purpose of any modulation is to vary the stimulation provided to the subject. Stimulation appears to be a function of the following:
a. The modulation or lack thereof (e.g., a continuous wave) on the incident laser beam or other stimulation source.
b. The wavelength of the laser affects the penetration depth into the skin surface (as well as underlying tissue) and may affect different photosensitive electrolyte compounds differently. It is also suspected that the compressive acoustic wavelength of ultrasonic sources and the electromagnetic wave (e.g., transverse wave, per Maxwells equations) may have some bearing on the overall stimulation of the patient.
c. The location of the incident laser beam or other type of source on the skin surface.
d. The pattern created in the nervous system when multiple laser beams and/or other stimulation sources are used simultaneously on the patient.
e. The power level of the energy beam and the duration that the beam is applied to the subject.
It should be noted that safety (principally eye safety) is a major factor in the use of any laser device. An implicit goal in the development of a laser and modulation system used for biostimulation is to minimize both the peak and the average beam energy required to effect a given type of stimulation. It is clear that most of the devices currently on the market have ignored this factor. As a result, many devices exist which constitute a potential eye hazard if improperly employed. Moreover, a few of the latest devices have sufficient beam energy where damage to skin cells may be concurrent with improper use.
Non-laser, non-electrical stimulation sources are principally of the diathermy (e.g., high frequency electromagnetic waves) and ultrasound (e.g., ultrasonic acoustic wave types). When employed in a pulsed mode both are generally gated at twice the line frequency (e.g., 100 Hertz in Europe and 120 Hertz in North America). Electromagnetic sources, while quite rare, generally appear to employ some form of the aforementioned binary scaled modulation.